Employee Benefit Plans (Quarterly Info) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	$ 15	$ 10	$ 44	$ 30
Interest cost	14	15	43	46
Expected return on plan assets	(19)	(19)	(56)	(57)
Amortization of net actuarial loss	11	10	32	29
Net actuarial loss from settlements	1	0	1	0
Net periodic benefit cost (credit)	22	16	64	48
Employer contributions			63
Estimated future employer contributions in current fiscal year			2
Other Postretirement Benefits [Member]
Components of net periodic benefit cost:
Service cost	0	0	1	1
Interest cost	3	2	7	7
Expected return on plan assets	(3)	(3)	(9)	(9)
Amortization of net actuarial loss	0	0	1	0
Reclassification to regulatory liability	1	1	3	3
Amortization of prior service cost (credit)	(4)	(5)	(12)	(15)
Net periodic benefit cost (credit)	(3)	(5)	(9)	(13)
Amortization of prior service cost (credit) from regulatory assets (liabilities)	$ (3)	$ (3)	(8)	$ (9)
Employer contributions			5
Estimated future employer contributions in current fiscal year			$ 1